CVE-2016-4461

aka Forced Double OGNL Evaluation

CVE: CVE-2016-4461
CWE: 20
bugs: []
vccs:
- note: Initial implementaiton for allowed methods when executing OGNL actions. Probable
    root cause component of predecessor vulnerability CVE-2016-0785 due to lackluster
    input sanitization.
  commit: f54afdc3f441dc48d012aebd3cbbdcd542811cee
- note: Sign of early efforts to mitigate double evaluation by disabling the evaluation
    expression altogether. This underscores issues with OGNL's evaluation expression
    during S2-029.
  commit: 61a7ee296161bbfa61e90871649598a2e4a680a2
- note: Enables expression evaluation and storage without input validation
  commit: 15857a69e7baf3675804495a5954cd0756ac8364
fixes:
- note: Introduces more restrictive SMI (Strict Method Invocation) - ActionConfig.java
  commit: 9ac863b339a3513dabd417f4be8a802418a997ba
- note: Adds additional blocked classes - struts-default.xml
  commit: 016b8eedd5ca47fce95e2a16069e640e3842906d
- note: Uses isSequence flag to block chained expressions - OgnlUtil.java
  commit: f238cf4f1091be19fbcfd086b042c86a1bcaa7fc
- note: Throws away methods that don't match pattern for allowed actions - DefaultActionMapper.java
  commit: 27ca165ddbf81c84bafbd083b99a18d89cc49ca7
- note: Disallow dot (.) in action name - DefaultActionMapper.java
  commit: 9b34a28190b71f73c26564ce06139aa4e4861e18
- note: Introduces new callMethod() function to execute actions (cherry pick commit
    b28b78) - DefaultActionInvocation.java, OgnlUtil.java
  commit: 7da4ef39023bb5d86509d65565a04b533e8b4c55
bounty:
  amt: 
  url: 
  announced: 
lessons:
  yagni:
    note: 
    applies: 
  question: |
    Are there any common lessons we have learned from class that apply to this
    vulnerability? In other words, could this vulnerability serve as an example
    of one of those lessons?
    Leave "applies" blank or put false if you did not see that lesson (you do
    not need to put a reason). Put "true" if you feel the lesson applies and put
    a quick explanation of how it applies.
    Don't feel the need to claim that ALL of these apply, but it's pretty likely
    that one or two of them apply.
    If you think of another lesson we covered in class that applies here, feel
    free to give it a small name and add one in the same format as these.
  serial_killer:
    note: 
    applies: 
  complex_inputs:
    note: Nature of forced double evaluation is a result of the complexity of inputs
      offered by OGNL's syntax
    applies: true
  distrust_input:
    note: Lack of overall input sanitization for expression evaluations
    applies: true
  least_privilege:
    note: 
    applies: 
  native_wrappers:
    note: 
    applies: 
  defense_in_depth:
    note: Lack of input sanitizaiton beyond initial input collection shows lack of
      defense in depth.
    applies: true
  secure_by_default:
    note: Failure to consider malicious use of forced expression evaluations using
      OGNL "%{}" syntax.
    applies: true
  environment_variables:
    note: 
    applies: 
  security_by_obscurity:
    note: 
    applies: 
  frameworks_are_optional:
    note: Failure to consider ramifications of expression evaluation syntax such as
      "%{}"
    applies: true
upvotes: 
mistakes:
  answer: "Overall, this vulnerability stems from failure to consider the security
    principle of \"secure by default\".\nFailure to consider malicious use of the
    OGNL language, especially when forcing expression evaluations \nusing \"%{}\"
    syntax, shows that adequate threat modeling was not done in preparation for integrating
    with this feature.\nLikewise, failure to account for potential malicious inputs
    when executing expressions signifies a lack of\nconsideration for the increased
    attack surface that results from complex inputs.\nConsidering the predecessor
    issue \"S2-029\" was supposed to be fixed in the version 2.3.28 release, the\nfact
    that the same issue re-appeared as \"S2-036\" proves a lack of understanding in
    regards to the core issue.\n"
  question: |
    In your opinion, after all of this research, what mistakes were made that
    led to this vulnerability? Coding mistakes? Design mistakes?
    Maintainability? Requirements? Miscommunications?
    Look at the CWE entry for this vulnerability and examine the mitigations
    they have written there. Are they doing those? Does the fix look proper?
    Use those questions to inspire your answer. Don't feel obligated to answer
    every one. Write a thoughtful entry here that those in the software
    engineering industry would find interesting.
nickname: Forced Double OGNL Evaluation
reported: '2016-05-02'
announced: '2016-06-17'
subsystem:
  name: ognl
  answer: Action Config, Struts Default Config, OGNL Util class, Default Action Invocation
  question: |
    What subsystems was the mistake in?
    Look at the path of the source code files code that were fixed to get
    directory names. Look at comments in the code. Look at the bug reports how
    the bug report was tagged. Examples: "clipboard", "gpu", "ssl", "speech", "renderer"
discovered:
  date: '2016-05-02'
  answer: Reported by Alvaro Munoz (alvaro.munoz@hpe.com)
  apache: false
  contest: 
  question: |
    How was this vulnerability discovered?
    Go to the bug report and read the conversation to find out how this was
    originally found. Answer in longform below in "answer", fill in the date in
    YYYY-MM-DD, and then determine if the vulnerability was found by a Apache
    employee (you can tell from their email address). If it's clear that the
    vulnerability was discovered by a contest, fill in the name there.
    The "automated" flag can be true, false, or nil.
    The "apache" flag can be true, false, or nil.
    If there is no evidence as to how this vulnerability was found, then you may
    leave the entries blank except for "answer". Write down where you looked in "answer".
  automated: false
description: "This vulnerability stems from improper input validation within Apache
  Struts\nin relation to OGNL, more formally known as Object Graph Navigation Language.\nOGNL
  is an expression language used to access and mutate Java Object properties,\nas
  well as interact with other forms of metadata.\nIn this instance, OGNL's expression
  evaluation operator \"%{}\" can be used to force\ndouble evaluation of a Struts
  data object attribute. Double evaluation is when an expression string is\nevaluated
  as code such that its output is also evaluated as code. Without a defined base case,
  this\nprocess can recurse indefinitely.\nWith respect to Apache Struts, a malicious
  actor can provide a string containing \"%{}\" that,\nwhen evaluated at a later point
  in time, forces double evaluation. In the event a malicious actor\nencodes program
  instructions within their provided string input, this vulnerability allows for\narbitrary
  code execution within the system.\nIt is important to note that this vulnerability
  stems from an incomplete solution to a prior issue\nin Apache version 2.3.28, classified
  as S2-029 in Apache's wiki (CVE-2016-0785). \n"
unit_tested:
  fix: true
  code: true
  answer: Fixes either introduced new tests or refactored legacy tests to account
    for changes.
  question: |
    Were automated unit tests involved in this vulnerability?
    Was the original code unit tested, or not unit tested? Did the fix involve
    improving the automated tests?
    Write the reasoning behind your answer in the "answer" field.
    For the "code" answer below, look not only at the fix but the surrounding
    code near the fix and determine if and was there were unit tests involved
    for this module. Must be just "true" or "false".
    For the "fix" answer below, check if the fix for the vulnerability involves
    adding or improving an automated test to ensure this doesn't happen again.
    Must be just "true" or "false".
future_fixes:
- note: 
  commit: 
curation_level: 1
previous_fixes:
- note: Restores excluded classes to structs-default.xml, reverting prior change that
    allowed these classes.
  commit: 4271682d2b944e9022e4e4c499df43e0ce7e58fd
- note: Fixes SMI with ActionConfigMatcher (WW-4596) for stricter action execution
  commit: 23a0c9eb643c41f800dc43159672dd31a6159472
CWE_instructions: |
  Please go to cwe.mitre.org and find the most specific, appropriate CWE entry
  that describes your vulnerability. (Tip: this may not be a good one to start
  with - spend time understanding this vulnerability before making your choice!)
security_bulletin: S2-036
bounty_instructions: |
  If you came across any indications that a bounty was paid out for this
  vulnerability, fill it out here. Or correct it if the information already here
  was wrong. Otherwise, leave it blank.
interesting_commits:
  answer: the following are interesting due to ther role in preventing this vulnerability
    from reoccuring.
  commits:
  - note: Allows developers to redefine regex used to match allowed methods when SMI
      is disabled.
    commit: 02b207fca529627f3a34660de86b51444461a7d2
  - note: Turn on SMI by default
    commit: 6da61ffdd7577ebaa43ced8189cc971519950b0b
  - note: Improved logging to assist with tracking allowed methods
    commit: bb9df6c7d3d499d09d6406397aacb12e455d2852
  - note: Add allowed methods to ActionBuilder to assist with mitigating illegal expressions
    commit: 0d92fd0ee5d4c23aabe7bf3c2ef1b30ff3e5c00d
  - note: Add GlobalAllowedMethods getter to PackageConfig and modified getActionConfig
      method in ConventionUnknownHandler
    commit: dd3b80f2be6feb72de808087edcf7914e9d5bb6b
  - note: Adds more informative messages when method is not allowed, addresses WW-4640
    commit: 1afb48aa765a96a9d183bb4ac249bfcc8f7daf3a
  - note: Improves validation RegEx for URLs
    commit: a0fdca138feec2c2e94eb75ca1f8b76678b4d152
  - note: Apache Struts version 2.3.29 RELEASE
    commit: bb22c585b5b52967fab033dba02cd244cd5b5b7a
  question: |
    Are there any interesting commits between your VCC(s) and fix(es)?
    Write a brief (under 100 words) description of why you think this commit was
    interesting in light of the lessons learned from this vulnerability. Any
    emerging themes?
    If there are no interesting commits, demonstrate that you completed this section
    by explaining what happened between the VCCs and the fix.
curated_instructions: |
  If you are manually editing this file, then you are "curating" it. Set the
  entry below to "true" as soon as you start. This will enable additional
  integrity checks on this file to make sure you fill everything out properly.
  If you are a student, we cannot accept your work as finished unless curated is
  set to true.
upvotes_instructions: |
  Students: when initially writing this, ignore this upvotes number.
  Once this work is being reviewed, you will be giving a certain amount of
  upvotes to each vulnerability you see. Your peers will tell you how
  interesting they think this vulnerability is, and you'll add that to the
  upvotes score on your branch.
nickname_instructions: |
  Nickname is optional. Provide a useful, professional, and catchy nickname for
  this vulnerability. Ideally fewer than 30 characters. This will be shown
  alongside its CVE to make it more easily distinguished from the rest.
reported_instructions: |
  Was there a date that this vulnerability was reported to the team? You can
  find this in changelogs, blogs, bug reports, or perhaps the CVE data.
  Please enter your date in YYYY-MM-DD format.
announced_instructions: |
  Was there a date that this vulnerability was announced to the world? You can
  find this in changelogs, blogs, bug reports, or perhaps the CVE data.
  Please enter your date in YYYY-MM-DD format.
fixes_vcc_instructions: |
  Please put the SVN commit number in "commit" below, and any notes about how this
  was discovered in the "note" field.
description_instructions: |
  You can get an initial description from the CVE entry on cve.mitre.org. These
  descriptions are a fine start, but they can be kind of jargony.
  Rewrite this description in your own words. Make it interesting and easy to
  read to anyone with some programming experience. We can always pull up the NVD
  description later to get more technical.
  Try to still be specific in your description, but remove Struts-specific
  stuff. Remove references to versions, specific filenames, and other jargon
  that outsiders to Struts would not understand. Technology like "regular
  expressions" is fine, and security phrases like "invalid write" are fine to
  keep too.
incomplete_fix_instructions: |
  Did the above "fixes" actually fix the vulnerability?
  Please list any fixes for the same issue before and after
  this CVE below.